Drilled nonported vacuum drum

ABSTRACT

Such a drum requires no porting and will accommodate webs of varying widths, some of which may not completely cover all holes in the drum surface. The present invention relates to a novel drilled, nonported vacuum roll for conve   A vacuum drum for gripping and feeding a web has its periphery provided with a pattern of drilled holes each having a diameter of 0.060 inches or less, said pattern of holes having a distribution such that nd2 V is not less than 0.05 or more than 0.15

United States Patent [72] Inventor John A. Rau

Portland, Oreg. [21] Appl. No. 46,946 [22] Filed June 17, 1970 [45] Patented Dec. 28, 1971 [73] Assignee Eastman Kodak Company Rochester, N.Y.

54] DRILLED NON-PORTED VACUUM DRUM 9 Claims, 14 Drawing Figs.

[52] US. Cl 226/95 [51] Int. Cl B6511 17/30 [50] Field of Search 226/7, 95, 97

[56] References Cited UNITED STATES PATENTS 2,837,330 6/1958 Lawrance et al. 226/95 3,125,265 3/1964 Warren et a1. 226/95 X 3,204,843 9/1965 Pendleton 226195 3,521,802 7/1970' Bossons Primary ExaminerAllen M. Knowles Attorneys-Walter 0. Hodsdon and Karl T. Naramore ABSTRACT: A vacuum drum for gripping and feeding a web has its periphery provided with a pattern of drilled holes each having a diameter of 0.060 inches or less, said pattern of holes having a distribution such that is not lessthaniltJ S or- Such a drum requires no porting and will accommodate webs of varying widths, some of which may not completely cover all holes in the drum surface.

S/ C M LINE Lia/Iii; W

DR LLED .NQN- F KT V QUUM DRUM The present invention relates to a novel drilled, nonported vacuum roll for conveying web material BACKGROUND OF THE INVENTION Vacuum drums are used in web conveying machines. Their function is to hold the web firmly to their surface, without slip between the web and the drum, thus controlling the speed of the web, and/or isolating the entering tension from the leaving tension. In the photographic industry, vacuum drums are used to handle webs l6mm. to at least 55 inchesin width, and at speeds to at least 1,000 f.p.m.

There are two general types of vacuum drums which are commonly used. One, the older of the two, has drilled holes through its shell. Vacuum is supplied to the holes from the drum interior as the drum rotates. The holes used in such drums are so large (A to 3/16 inches diameter) that a porting, or rotary valving system is assigned the switching function of disconnecting the vacuum supply from that portion of the drum not covered by the web. The other type of vacuum drum is made from a porous material and uses no porting. Air is pulled through the pores even in those areas not covered by the web.

The porous material vacuum drum has a very simple configuration. It consists of a she made from some porous material. The shell is closed at both ends by means of gudgeons, one or both of which accommodates bearings so that the drum can turn. Vacuum is supplied to the center of one or both drum ends by means of a simple rotary joint. Advantages of the porous drum are its simplicity of construction, its relatively low cost (though the porous material is expensive), and its ability to accommodate webs of varying width. Its disadvantages are its tendency to plug up with use (because the small pores make it an air filter); the difficulty in keeping it clean (because each pore is a potential trap for dirt or contaminants and, having trapped such matter, is next to impossible to clean); the need for special and expensive machining techniques to finish the drum surface without closing the pores; and the need to depend upon a relatively short source of supply for the porous material.

The ported vacuum drum comprises two basic assemblies: the rotating shell and a stationary porting or valving unit. The shell is perforated with holes which communicate with the porting system in such a way that, only when a hole is covered by the web is the hole connected to the vacuum supply. Porting systems are of two types: one is a stationary core inside of the rotating drum, the other has stationary end plates. The drum surface may be grooved or channelled to improve its high-speed performance. Disadvantages of a ported drum include its complexity and consequent high cost, and its inability to accommodate webs of different widths unless the porting system is made axially adjustable, and hence is even more complex and costly.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide a drilled, nonported vacuum drum which combines the advantages of both of the above described known vacuum drums and has none of their disadvantages. It can be made from commonly available material, no special shop skills are required in its fabrication, its design is simple, it is easily kept clean, it can be given a polished surface so as not to damage the web passed thereover, it is usable with webs of varying widths, and is relatively inexpensive. l have found that if vacuum is supplied to the drum surface by a minimum number of small holes, e.g., less than 0.060 inches in diameter, and the vacuum is spread on the drum surface by a system of closely spaced small grooves, then no porting of the drum is required and such a drum will accommodate webs of varying widths, some of which may not completely cover all of the grooves in the drum surface.

The novel features which I consider characteristic of my invention are set forth with particularity in the appending claims. The invention itself, however, both as to its organization and its methods of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings in which:

DESCRIPTION OF DRAWINGS FIG. I is a longititudinal view of a drilled vacuum drum, partly in section;

FIGS. 2-10 are developed views of portions of vacuum drums having hole and groove patterns according to different embodiments of the present invention;

FIG. 11 is an enlarged sectional detail showing the preferred shape of the grooves;

FIGS. 12 and 13 are enlarged schematic views showing the relative holding power and characteristics of wide and narrow grooves on a web; and

FIG. 14 is a graph showing how the vacuum efficiency of a typical porous vacuum drum and a drilled nonported grooved drum according to the present invention varies with web speed.

DESCRIPTION OF PREFERRED EMBODIMENTS In order to demonstrate the novelty of the present drilled, nonported vacuum roll, it is desirable to briefly describe how and why a vacuum drum operates.

Vacuum drums are used where it is necessary to separate two tensions in a web machine. The tension in the web entering the drum may be higher or lower than that leaving the drum. Textbooks of elementary mechanics give a formula which relates the two tensions (T =the higher and T qhe lower) to the wrap, 0, of the web around the drum and to the coefficient of static friction, f between the web and the drum. The formula is:

T JT =e fiwhere (e=2.7l828 ---)(l) As long as the two tensions, which a drum or roller is called upon to isolate, do not exceed the ratio given above, a vacuum drum is not rs t siwm Mwwm... V.

Larger tension ratios can be permitted if a vacuum is supplied to the web-drum interface. Then atmospheric pressure acting on the outside face of the web causes a pneumatic pressure difference to exist across the web thickness. This increases the contact pressure between the web and the drum and consequently increasesthe frictional force between the web and the drum. If V is the interface vacuum, measured in inches of Hg, averaged over the entire area of contact; W is the web width, and D is the drum diameter, then the following relationship can be shown to exist:

' T =T ef0+ A V WD (ef6-1) (2) It should be noted that V H in the above formula is the average effective vacuum in the webdrum interface, measured in inches of Hg. Its value is lower than that applied internally to the drum because of the following: 1. In ill centering nip, where the incoming web first contacts the drum, air is trapped in the interface between the drum and the web. This air is at atmospheric pressure or even slightly higher in pressure. The vacuum inside of the drum does not become effective until this interfacial air has been sucked away.

2. Contact between the web and the drum has the effect of preventing air flow in the web-drum interface. Thus points on the web contacting the drum which are removed from the vacuum sources on the drum surface do not reach the drums internal vacuum supply in the time available during which those points are in contact with the drum. Flow must take place in the web-drum interface and there must be sufficient flow to result in reasonable values of V,,-. In order to utilize equation (2) we define:

V =k V, Where k (vacuum efficiency) is an experimentally determined constant which depends upon the effectiveness of vacuum spreading in the web-drum interface and V, is the drum internal vacuum.

In an experiment run with a typical porous drum, k" remained constant at about 70 percent up to a web speed of about 1,500 f.p.m., then dropped off rapidly to reach 40 percent at 2,000 f.p.m. It is reasonable to assume that k" would have a continued drop below 40 percent beyond 2,000 f.p.m., but this was the highest speed the machine was capable of. In contrast to this, a typical drilled nonported drum construction in accordance with the present invention still had a value of k 50 percent at 2,000 f.p.m. with no evidence of it dropping off at higher speeds. The surprising result is depicted in FIG. 14 and its probable cause will be described further below.

For good high-speed performance, it is important that the evacuation of the interface take place rapidly. Two things are necessary to do this.

1. The airflow rate throughthe uncovered surface of the drum should be of the order of several cubic feet per minute, per square foot of drum surface.

2. That flow paths from all points in the web-drum interface to the nearest hole or groove be short (less than 0.05 inches).

The first requirement is satisfied by having adequate size and number of holes through the drum surface for drilled drums and by adequate porosity for porous drums. The second requirement is satisfied by using a larger number of holes per unit of surface area or by using a system of grooves for drilled drums and is automatically satisfied for porous drums.

Consider now a drilled drum as schematically shown in FIG. 1. The drum is simply a closed shell with vacuum supplied to one or both ends and with a pattern of holes 11 extending through the drum surface. When vacuum is supplied to the drum, with the holes uncovered, air will flow through the holes into the drum. If this drum has holes as large as used in conventional drilled drums (0.I25-0.I875 inches diameter) porting is required because the amount of airflow into the drum when all of the holes are uncovered will lower the vacuum in the drum interior below a value which would provide any holding power (V, will be too low) while such a condition, in which all of the holes are uncovered, is not a normal running condition, it is desirable that even with all ofthe holes uncovered the drum should be able to hold a film to its surface in order to assist threading up. If, on the other hand, the resistance to flow offered by all of the holes in the drum surface is considerably greater than the resistance of flow offered by the vacuum supply line from the drum interior to the vacuum pump, then the vacuum in the drum interior will not be much lower than the supply line vacuum (V," will be high When a web is placed on such a drum, blocking the airflow into some of the holes, the drum internal vacuum will approach closer to the line vacuum. Thus the drums internal vacuum is lowest when the drum is completely uncovered. This is the worst web holding case since web holding ability is a direct function of the drum internal vacuum level. Therefore, if the air flow resistance offered by the holes in a drilled drum is significantly larger than the airflow resistance offered by the vacuum supply line, then no porting will be required. This discovery is the basis of the present invention as will be described in detail hereafter.

A drilled, nonported vacuum drum according to the present invention is essentially like the vacuum drum shown in FIG. I, but has the following unique features schematically illustrated in FIGS. 2-10 where a developed portion of vacuum drums constructed according to different embodiments of the present invention are illustrated.

I. Vacuum is supplied to the drum surface 10' by a minimum number of small holes 11'. By small holes, I mean holes which are less than 0.060 inches in diameter.

2. Vacuum is spread over the drum surface by a system of closely spaced small grooves, I2.

Holes less than 0.060 inches in diameter are used because they have been found to be sufficiently strong restrictors of air flow compared to conventional vacuum supply lines, and yet when they are properly spaced on the surface of the drum they allow sufficient flow to allow good high web speed operation.

By using a few small holes to conduct the vacuum from the drum interior to the drum surface, one can provide sufficient flow and yet meet the requirements that the drum surface be, by far, the greatest flow restriction in the system. With several different experimental drums having these characteristics, the drum internal vacuum was never less than 75 percent ofit line vacuum even with the drum surface completely uncovered.

It has been found that good high-speed performance is obtained economically with drilled, nonported drums for which nd'Wlies between the limits of 0.05 and 0.15 where n number of holes per square foot ofdrum surface d diameter of the holes in inches V= vacuum inside the drum with all holes uncovered, measured in inches of Hg.

The air flow rate per square foot of exposed drum surface is given by $65 ndfiin units of standard cubic feet per minute.

The groove system in order that it work well, that is, result in high efiiciencies, should be composed of small, closely spaced parallel grooves. Good results, vacuum efficiency 50 percent, have been obtained with groove spacing of IS grooves per inch where the grooves were triangular in cross section 0.010 inches deep and 0.10 inches wide, as shown in FIG. 2. The exact cross-sectional shape of the groove is not important. Experiments have shown that wide grooves hold only slightly better than narrow grooves (at the same vacuum level) and that thin webs are held slightly better than thick webs.

It is perhaps surprising that groove width has so little effect on web holding. This can be explained by considering FIGS, 12 and 13.

In case of the wide groove shown in FIG. 12 the vacuum is sealed off at the edges of the groove while for a narrow groove shown in FIG. I3, the vacuum extends for a considerable distance beyond the groove edges. If the areas under both vacuum profile curves are equal, the'web holding ability of both grooves would be equal. Based on the measured vacuum holding ability of five different width grooves experimented with, this area appears to decrease only slightly in progressing from grooves 0.030 inch wide to grooves 0.005 inch wide. If a very thin web is placed on a 0.030 inch wide groove, the web can be seen sealing on the groove edges, see FIG. 12. If it is placed on a 0.005 inch groove, the vacuum can be seen spreading out about one-half inch from the groove edges, see FIG. 13. It follows from this that the use of narrow grooves has less tendency to mark the surface of the web due to a tendency to draw the web into the grooves. This factor is particularly important when thin flexible webs are being used.

As shown in FIGS. 2-10, a feed slot 13 deeper and/or wider than the grooves I2 is used to connect the holes 11' to the grooves. Either axial or circumferential grooves may be used as shown in FIGS. 2 and 3 respectively. Circumferential grooves are more suited to large wrap angles where leakage into the groove system at the web nips is not a major factor.

The highest web holding ability is obtained when the web completely covers the groove system. Therefore, it is best to design the groove system so that it is completely covered by the web in the axial direction of its drum. Sometimes in variable width drums this may not be possible. In this case, as long as the web always covers at least those holes in the drum which feed the grooves under the web, and as long as the grooves are small as specified in the design procedure set forth below, the web holding ability will not decrease to less than one half of the value it would have been if the groove system had been completely covered. Thus, by following a few simple design procedures, grooved, nonported vacuum drums according to the present invention can be designed which have all of the advantages of drilled drums with none of their disadvantages. In addition, grooved, nonported drums can be designed for use with variable web widths as will now be described.

The design of groove systems for a variable web width drum will be illustrated by discussing hole and groove systems for use on a drum that will handle two web widths where both webs are referenced to one side of the drum. FIG. 4 shows a design using axial grooves 12 and FIG. 5 shows a design using circumferential grooves 12. Note that when the narrow web is running on the drum, more holes in the drum are open to the atmosphere than when the wide web is running; but since small holes are used, this has a very small effect on the drum internal vacuum.

If the narrow web cannot be referenced to one side of the drum, it can run in any axial position where the web will cover at least one circumferential row of holes. Since this then allows air leakage along the edges of the web into the groove system a loss in web holding ability will result. it has been found that this loss will not be more than one-half of the web holding ability with the groove system completely covered if:

a. Groove width and depth does not exceed 0.010 inch,

b. The axial distance between either edge of the web and any hole supplying vacuum to that web does not go below 1 inch.

in designing a vacuum drum according to the present invention the following principles should be followed:

1. Decide on hole diameter, (d), the number of holes per square foot (n)and vacuum (V) so that O.05 nd O.15 where V is the vacuum inside bf the drum with all holes uncovered. it should be noted that drum wall thickness is not a factor in the range of 0.125 inch to 0.750 inch. in the interest of good high speed performance, it is best to keep the diameter of the holes (d) small and let the hole density (n) be high. Hole diameter (d) should not be more than 0.060 inch.

2. The holding power of the drum can then be predicted by T,,=T,, e"+%kvwD(e -1) where k should conservatively b5 taken as 0.50 or less, and where T tension on the high-tension side of the drum in lbs.

T, tension on the low-tension side of the drum in lbs.

f static coefficient of friction between the drum and web (lb./lb.) 0= angle of wrap in radians e 2.718 V= vacuum in the drum with all holes uncovered (inches of W= web width (inches) D=drum diameter (inches) 3. The airflow requirement of the drum at the indrum vacuum specified, will then be (standard cubic feet per minute) Q=65nd wl V 4. Provide channels and grooves on the drum surface so that the distance from any point on the drum surface to the nearest groove is not more than 0.050 inches. The requirement is met by a pattern of grooves spaced l0 grooves to the inch or closer. Groove width and depth are not critical, but the groove width for thin web should be small. Depths and widths from 0.010 to 0.015 inches have given good performance. The shape of the groove cross section is immaterial.

5. Decide on a groove pattern as recommended below. Locate the holes in the groove pattern so that they are equally spaced circumferentially, and so that the hole pattern is symmetric with respect to the web centerline. Provide appropriate feed grooves as part of the groove pattern. Feed grooves should be larger in cross section than the vacuum spreading grooves to assure adequate flow capacity. This is best done by making the feed grooves deeper.

6. Groove patterns may be arranged either axially or circumferentially of the drum. Circumferential patterns are easily cut on a lathe, axial grooves require milling or shaping. Either can be produced by chemical etching. Circumferential grooving should not be used with wrap angles of less than 90.

7. For variable web-width drums, the overall groove pattern must be subdivided into subpatterns in such a way that, in those areas of the drum which may or may not be covered depending upon web width, each hole has its own subpattern or grid which communicate little, or not at all, with the grids of other holes. The area of the drum which is covered by even the narrowest web may be designed like any nonvariablewidth drum.

8. if there is to be a large number of web widths, it may be advantageous to design the groove pattern so that some of the grooves are not covered over their entire length for some of the web width. It has been found that an open-ended groove still provides useful holding power if the open end is at least one inch from the nearest hole communicating with it, and if the cross-sectional area of the hole is at least five times that of the groove.

FlGS. 6-10 are illustrations of several drums which have been built and satisfactorily tested. The drum shown in FIG. 6 has a diameter of 7.5 inches, a width of 3 inches, has V grooves 0.030 inches wide, spaced 1 l grooves to the inch. This drum had a value of k of 50 percent for an axially fully covered groove pattern.

The drum shown in FIG. 7 has a diameter of 7.5 inches, a width of 3 inches, has V grooves 0.010 inches wide, spaced 14.3 grooves per inch. The k" of this drum for an axially fully covered groove pattern was 65 percent.

The drum shown in FIG. 8 has a diameter of 6 inches, a width of 3 inches, and V grooves 0.010 inches wide, spaced l5 grooves per inch. Forthis drum, k=40-50 percent for an axially fully covered groove pattern.

The drum shown in FIG. 9 is a variable width one having a diameter of 6 inches, a width of 10 inches, and V grooves 0.010 wide space 15 grooves per inch. This drum showed a k of 40-50 percent for an axially fully covered groove pattern.

The drum shown in FIG. 10 had a drum diameter of 7.5 inches, a drum width of 3 inches, and chemically milled grooves 0.007 inches wide and spaced 25 grooves per inch. With an axially fully covered groove pattern this drum showed a k of 65 percent.

FIG. 14 shows and compares vacuum efficiency as a function of web speed for a porous drum and the drilled, nonported drum of the present invention. in each instance, the drums were 8 inches in diameter, they were fully covered by a 70 mm. web, and they both had approximately the same interior vacuum, e.g., 2 inches of Hg. These curves show that the porous drum has an efficiency of 70 percent over the speed range of 0-l,500 f.p.m. and starts dropping off rapidly at higher speeds. The grooved, nonported drum has an efficiency of approximately 50 which remains constant over the test speed range (to 2,000 f.p.m.

The reason that the porous drum is more efficient than the grooved drum is that its vacuum sources (pores) are more closely spaced and more numerous than the vacuum sources (grooves) of the grooved drum. The efficiency of both drums respond differently to increasing speed. The porous drum has a substantially constant vacuum efficiency throughout most of the test web speed; however, it does lose efficiency at high web speeds. This efficiency loss probably results because the drum flow capacity is taxed by the increased amounts of boundary layer air associated with high web speeds. in contrast, vacuum efficiency for the grooved drum remains substantially constant at 50 percent at high speeds, rather than showing a drop off at high speeds because its flow capacity is large enough to handle the associated boundary layer airflow at high speeds.

From the above description, it will be apparent that a grooved, nonported vacuum drum made in accordance with the present invention provides a vacuum drum design which has all of the advantages of both porous and drilled drums with none of the disadvantages of either of them. The novelty of the present vacuum drum lies not so much in the use of holes and grooves per se, but in the proportioning of the dimensions of the holes and grooves in such a way as to obviate the necessity for complex porting arrangements used in conventional drilled drums to shut off the vacuum from that portion of the drum surface which is not covered by the web.

The invention has been described in detail with particular reference to the preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

1 claim:

1. A web-feeding roll for gripping a web by suction comprismg a. a closed drum at least one end of which is adapted to be connected to means for producing a partial vacuum within the interior of said drum;

b. the periphery of said drum provided with a pattern of holes extending directly from the interior of the drum to the surface of the drum,

1. the diameter of each of said holes being 0.060 inches or less; and 2. said pattern of holes having a distribution such that nd j-{V is not less than 0.05 nor greater than 0.15 where V the vacuum inside the drum with all holes uncovered (inches of Hg) d= the diameter of the holes (in inches) n the number of holes per square foot of drum surface.

2. A web-feeding roll according to claim 1, and including a first series of narrow and shallow grooves in the surface of said drum and arranged in substantially parallel relation over the entire drum surface; and a second series of grooves in said drum surface having a larger cross section than the grooves of said first series, each of the grooves of said second series extending from a hole and at an angle through and across the grooves of said second series to place the grooves of said first series in communication with said holes for spreading the suction over the drum surface.

3. A web-feeding roll as defined in claim 2, wherein said grooves of the first series are spaced 0.1 inches a part or less.

4. A web-feeding roll as defined in claim 3, wherein said grooves of the first series are substantially 0.01 inches wide and 0.01 inches deep.

5. A web-feeding roll according to claim 2, wherein the holes are located in the groove pattern so that they are equally spaced circumferentially of the drum and so that the hole pattern is symmetric with respect to the centerline of the web to be fed by the roll.

6. A web-feeding roll according to claim 2, wherein the first series of grooves are arranged to extend circumferentially of the drum surface.

7. A web-feeding roll according to claim 2, wherein the first series of grooves are arranged to extend axially of the drum surface.

8. A web-feeding roll according to claim 2, but adapted to feed variable width webs, characterized in that the overall groove pattern is subdivided into subpatterns in such a way that in those areas of the drum surface which may or may not be covered depending on web width, each hole has its own subpattern or grid which communicates little or not at all with the subpattern or grid of other holes.

9. A web-feeding roll according to claim 2, but adapted to feed variable width webs, characterize in that the groove pattern is arranged in such a way that the uncovered end of any groove, depending upon the width of the web passing over the drum, will be at least one inch from the nearest hole communicating with it and the cross-sectional area of the hole is at least five times that of the groove. 7 

1. A web-feeding roll for gripping a web by suction comprising a. a closed drum at least one end of which is adapted to be connected to means for producing a partial vacuum within the interior of said drum; b. the periphery of said drum provided with a pattern of holes extending directly from the interior of the drum to the surface of the drum,
 1. the diameter of each of said holes being 0.060 inches or less; and
 2. said pattern of holes having a distribution such that nd2 V is not less than 0.05 nor greater than 0.15 where V the vacuum inside the drum with all holes uncovered (inches of Hg) d the diameter of the holes (in inches) n the number of holes per square foot of drum surface.
 2. said pattern of holes having a distribution such that nd2 V is not less than 0.05 nor greater than 0.15 where V the vacuum inside the drum with all holes uncovered (inches of Hg) d the diameter of the holes (in inches) n the number of holes per square foot of drum surface.
 2. A web-feeding roll according to claim 1, and including a first series of narrow and shallow grooves in the surface of said drum and arranged in substantially parallel relation over the entire drum surface; and a second series of grooves in said drum surface having a larger cross section than the grooves of said first series, each of the grooves of said second series extending from a hole and at an angle through and across the grooves of said second series to place the grooves of said first series in communication with said holes for spreading the suction over the drum surface.
 3. A web-feeding roll as defined in claim 2, wherein said grooves of the first series are spaced 0.1 inches apart or less.
 4. A web-feeding roll as defined in claim 3, wherein said grooves of the first series are substantially 0.01 inches wide and 0.01 inches deep.
 5. A web-feeding roll according to claim 2, wherein the holes are located in the groove pattern so that they are equally spaced circumferentially of the drum and so that the hole pattern is symmetric with respect to the centerline of the web to be fed by the roll.
 6. A web-feeding roll according to claim 2, wherein the first series of grooves are arranged to extend circumferentially of the drum surface.
 7. A web-feeding roll according to claim 2, wherein the first series of grooves are arranged to extend axially of the drum surface.
 8. A web-feeding roll according to claim 2, but adapted to feed variable width webs, characterized in that the overall groove pattern is subdivided into subpatterns in such a way that in those areas of the drum surface which may or may not be covered depending on web width, each hole has its own subpattern or grid which communicates little or not at all with the subpattern or grid of other holes.
 9. A web-feeding roll according to claim 2, but adapted to feed variable width webs, characterize in that the groove pattern is arranged in such a way that the uncovered end of any groove, depending upon the width of the web passing over the drum, will be at least 1 inch from the nearest hole communicating with it and the cross-sectional area of the hole is at least 5 times that of the groove. 